TheNeuralBit commented on code in PR #258: URL: https://github.com/apache/parquet-format/pull/258#discussion_r1643310708
########## CONTRIBUTING.md: ########## @@ -29,3 +29,139 @@ Recommendations and requirements for how to best contribute to Parquet. We striv ### License By contributing your code, you agree to license your contribution under the terms of the APLv2: https://github.com/apache/parquet-format/blob/master/LICENSE + +### Additions/Changes to the Format + +Note: This section applies to actual functional changes to the specification. +Fixing typos, grammar, and clarifying concepts that would not change the +semantics of the specification can be done as long a comitter feels comfortable +to merge them. When in doubt starting a discussion on the dev mailing list is +encouraged. + +The general steps for adding features to the format are as follows: + +1. Discuss changes on the developer mailing list ([email protected]). + Often times it is helpful to link to a draft pull request to make the + discussion concrete. This step is complete when there is lazy consensus. Part + of the consensus is whether it sufficient to provide 2 working + implementations as outlined in step 2 or if demonstration of the feature with + a down-stream query engine is necessary to justify the feature (e.g. + demonstrate performance improvements in Arrow's DataSet library or Apache + Data Fusion or another open source engine). + +2. Once a change has lazy consensus, two implementations of the feature + demonstrating interopability must also be provided. One implementation MUST + be [parquet-java](http://github.com/apache/parquet-java). It is preferred + that the second implementation be + [parquet-cpp](https://github.com/apache/arrow) or + [parquet-rs](https://github.com/apache/arrow-rs), however at the discretion + of the PMC any open source Parquet implementation may be acceptable. + Implementations whose contributors actively participate in the community + (e.g. keep their feature matrix up-to-date on parquet-site) are more likely + to be considered. If discussed as a requirement in step one, demonstration + of integration with a query engine is also required for this step. The + implementations must be made available publicly, and they should + be fit for inclusion (for example, they were submitted as a pull request + against the target repository and committers gave positive reviews). + +Unless otherwise discussed, it is expected the implementations will be developed +from their respective main branch (i.e. backporting is not expected). + +3. After the first two steps are complete a formal vote is held on the Parquet + mailing list to officially ratify the feature. After the vote passes the + format change is merged into the parquet-format repository and it is expected + the changes from step 2 will also be merged soon after. Before merging into + Parquet-java a parquet-format release must be performed. + +#### General guidelines/preferences on additions. + +1. To the greatest extent possible changes should have an option for forwards + compatibility (old readers can still read files). + +2. New encodings should be fully specified in this repository and ideally not + rely on an external dependencies for implementation (i.e. `parquet-format` is + the source of truth for the encoding). + +3. New compression mechanisms must have a pure Java implementation that can be + used as dependency in parquet-java. + +### Releases + +The Parquet PMC aims to do releases of the format package only as needed when +new features are introduced. If multiple new features are being proposed +simultaneously some features might be consolidated into the same release. +Guidance is provided below on when implementations should enable features added +to the specification. Due to confusion in the past over Parquet versioning it +is not expected that there will be a 3.x release of the specification in the +foreseeable future. + +### Compatibility and Feature Enablement + +For the purposes of this discussion we classify features into the following buckets: + +1. Backwards compatible. A file written under an older version of the format + should be readable under a newer version of the format. + +2. Forwards compatible. A file written under a newer version of the format with + the feature enabled can be read under an older version of the format, but + some information might be missing or performance might be suboptimal. + +3. Forwards incompatible. A file written under a newer version of the format with + the feature enabled cannot be read under an older version of the format (e.g. + adding and using a new compression algorithm). Review Comment: One clarifying question here - does "cannot be read under an older version of the format" allow for "cannot be read _correctly_ under an older version of the format"? I suspect we want that be considered a breaking change. For reference I have the Arrow spec in mind which [defines](https://arrow.apache.org/docs/format/Versioning.html#forward-compatibility) forward compatibility as "An older client library must be able to either read data generated from a new client library or **detect that it cannot properly read the data.**" (emphasis mine). Is the "detect" case what we're calling "Forwards incompatible" here? -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. 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